While dolphins have been taught to mimic the pattern and durations of sounds in human speech, no animal has spontaneously tried such mimicry.
But researchers heard a nine-year-old whale named NOC make sounds octaves below normal, in clipped bursts.
The researchers outline in Current Biology just how NOC did it.
But the first mystery was figuring out where the sound was coming from. The whales are known as "canaries of the sea" for their high-pitched chirps, and while a number of anecdotal reports of whales making human-like speech, none had ever been recorded.
When a diver at the National Marine Mammal Foundation in California surfaced saying, "Who told me to get out?" the researchers there knew they had another example on their hands.